1. Field of the Invention
The present invention relates to a raw material used for production of GaAs single crystals or GaAs polycrystals by utilizing solidification of melt in a process such as the Czochralski method (drawing method).
2. Description of the Related Art
In recent years, various semiconductor devices such as LSI, lasers, and LED attain high density and high performance, thus realizing high performance and miniaturization of various electronic parts and electrical appliances. Particularly a GaAs substrate which works at a rate several times higher than silicon, consumes less electric power and is highly resistant to noises, is used often in high-speed and high-frequency elements such as FET, IC etc. This GaAs substrate is produced thorough slicing and various procedures for processing of single-crystal ingots grown by a process of utilizing solidification of melt, for example by the Czochralski method or Bridgman process.
When this GaAs substrate is used to form e.g. an optical film element, the density of carriers in the film layer should be reduced. For this reduction, As oxides present in As used as a starting material should be removed at the maximum degree in order to render As highly purified for production of GaAs single-crystal ingots. Further, a film of GaAs etc. is important as an element-separating film for electrically separating element base materials or elements from one another, and it is known that for making this kind of film highly resistant, transition metals such as iron and nickel are added to the film in order to utilize the deep orbital formed by these transition metals.
However, if As oxides are present in this kind of film, the film is prevented from becoming highly resistant, thus failing to achieve the desired characteristics. Further, if single-crystal ingots are produced from a material contaminated with As oxides by the Czochralski method, the As oxides remain as insolubles in the melt, thus preventing the melt from forming single crystals upon solidification, and thus single-crystal ingots having large diameters cannot be produced.
On the other hand, As is easily oxidized, and when left in the air, it reacts immediately with oxygen to form As oxides. Accordingly, when GaAs single crystals are produced by the Czochralski method, As used as the raw material is carried after introduction into an ampoule with an inert gas sealed therein, and just before use for production, the ampoule is opened and introduced into a crucible.
For the conventional production of GaAs semiconductors as described above, As i.e. one component in GaAs is easily oxidized so that in preventing As from contacting the air, it should be introduced into an ampoule for shipping, resulting in an increase in costs. Further, it is troublesome for the ampoule to be opened for taking As, and it is also problematic that As may be scattered upon opening of the ampoule. In addition, if the ampoule is opened in the air, oxidation of As is immediately initiated to form arsenious acid (AS2O3) on the surface of As before the crucible is filled with an inert gas.
The AS2O3 formed on the surface of As can be removed by heating As in the crucible under predetermined conditions, but this requires an additional heating step to lower productivity. In addition, toxic amorphous AS2O3 is generated by heating. Further, the AS2O3 removed should be dealt with.
Accordingly, the object of the present invention is to provide a raw material used for production of GaAs single crystals or GaAs polycrystals, which can be carried without requiring an ampoule etc. and without oxidizing As.
To achieve this object, the present invention provides a raw material for production of GaAs crystals which is used in production of GaAs single crystals or GaAs polycrystals by utilizing solidification of melt, wherein As is accommodated in the inside of Ga.
In another aspect, the present invention provides a raw material for use in production of GaAs single crystals or GaAs polycrystals by utilizing solidification of melt, wherein As is accommodated in a sealed space formed in the inside of Ga.
In this other aspect, the sealed space is preferably an inert gas atmosphere or a vacuum.
In the present invention, the purity of Ga and/or As is e.g. 99.9999% by weight or more. Because As is highly volatile and can partially volatilize during production of GaAs ingots, it is preferable that the ratio of As atoms to Ga atoms is selected suitably such that, for example, As/Ga becomes equal to or smaller than 1.5.
Since As is covered with Ga in the raw material of the present invention, As is not brought into contact with the air. Accordingly, the raw material can be carried without oxidizing As. The raw material of the present invention can be introduced as such into a crucible, then heated and melted, from which GaAs polycrystals and GaAs single crystals can grow by a process such as Czochralski or Bridgman process to produce single-crystal ingots. The GaAs single-crystal ingots thus produced serve as high-purity semiconductor material containing no or less As oxides, so that by slicing the GaAs single-crystal ingots produced, the most suitable high-purity GaAs substrate for production of high-density and high-performance semiconductor devices in recent years can be obtained.
According to the present invention, it becomes unnecessary to fill an ampoule with As prior to shipping, thus reducing the operation and realizing a reduction in costs, and further the procedure of opening the ampoule becomes unnecessary, thus facilitating production of GaAs single crystals. By previously regulating the amount of As and Ga constituting the raw material of the present invention, a desired amount of GaAs single crystals can be produced, and a waste of the starting materials can be eliminated.